Antioxidants are compounds that are added to organic materials to retard oxidation. Prominant among the general classes of compounds which can be used as antioxidants are sulfides, disulfides, sulfoxides, phosphites, amines, phenols, selenides and zinc dithiophosphates. Examples of such antioxidants include the hindered phenols such as 2,6-di-tertiary-butyl-4-methylphenol, 4,4'-methylene bis(2,6-di-tertiary-butyl phenol) and 4,4'-thiobis (2-methyl-6-tertiary-butyl phenol); and amines such as N-phenyl-alpha-naphthylamine, N-phenyl-beta-naphthylamine, tetramethyldiaminodiphenylmethane, anthranilic acid, phenothiazine and alkylated derivatives of phenothiazine. See, for example, U.S. Pat. Nos. 1,988,299; 2,000,045; 2,202,877; 2,265,582; 2,868,730; 3,032,502; 3,038,858; 3,038,859; 3,043,775; 3,065,178; and 3,132,103; Belgian Patent No. 634,220; and British Patent No. 873,066. Antioxidants are also disclosed in the following publications: "Organic Amines, Hydroxy Compounds Lead Among Anti-Oxidants for Lubricants," Byers, National Petroleum News, Feb. 10, 1937, pp. 67-70; "Lubricating Oil Additives--Oxidation Inhibitors and Detergents," Kalichevsky, Petroleum Refiner 28, No. 9, pp. 85-93, 1949; and "Antioxidants for High Temperature Lubricants," Stemniski et al, Amer. Soc. Lubric. Engineers Preprint No. 63 LC-13, 11 pp., Oct., 1963. These patents and publications are incorporated herein by reference.
While many of the foregoing antioxidants are meritorious, none have provided antioxidant characteristics that are entirely satisfactory. It would be advantageous to provide antioxidants that are more useful in lubricants, functional fluids, normally liquid fuels, emulsions of both the water-in-oil and oil-in-water type, aqueous compositions, and the like.